Dependence Of Heat Loss Research Articles

On the circulation heat losses in domestic hot water systems in residential buildings

The share of domestic hot water (DHW) systems in total energy consumption of buildings, especially in Nearly Zero-Energy Buildings (NZEBs), is rising and will continue doing so in the future, because most energy efficient measures are dedicated for heating/cooling systems. Besides, the amount of detailed field research on DHW systems is limited in comparison to heating/cooling systems. This article identifies the problem of excessive heat losses in the circulation lines of the DHW installation in residential buildings supplied from the district heating network. The analysis used the measurement and operational data for the summer season, i.e. the period of May–September 2018 for nine multi-family buildings located in Lublin (Poland). The buildings are divided into three groups according to the cubic volume: below 5000 m3, 5000 ÷ 10,000 m3 and above 10,000 m3. The research was conducted in two variants. Method I concerns the heat losses from circulation only at night and days, when hours with the power needed to heat DHW is lower than assumed values on the basis of DHW consumption, while method II covers all hours of the day. The obtained average results of circular heat losses range from 9.36 ÷ 25.38 % for method I and 22.96 ÷ 69.14 % for method II. The largest energy losses were recorded in the summer months, mainly August and July, while the smallest losses were recorded for May, June and September during the school year. The obtained calculations and their results are the basis for determining the information on the dependence of heat losses on circulation pipes and the size of buildings.

Thermal History of the Earth: On the Importance of Surface Processes and the Size of Tectonic Plates

AbstractGeochemical constraints on mantle temperature indicate a regular decrease by around 250 K since 3 Ga. However, models of Earth's cooling that rely on scaling laws for thermal convection without strong plates are facing a thermal runaway backwards in time, due to the power‐law dependence of heat loss on temperature. To explore the effect of surface dynamics on Earth's cooling rate, we build a two‐dimensional temperature‐dependent model of plate tectonics that relies on a force balance for each plate and on Earth‐like parameterized behaviors for the motion, creation, and disappearance of plate boundaries. While our model predicts the expected thermal runaway if plate boundaries are fixed, we obtain an average cooling rate consistent with geochemical estimates if the geometry of plate tectonics evolves through time. For a warmer mantle in the past, plates are faster but also larger (and less numerous) so that the average seafloor age and resulting heat flux always remain moderate. The predicted decrease in the number of plates backwards in time is in good agreement with recent plate reconstructions over the last 400 Myr. Our model also gives plate speed and subduction area flux consistent with these reconstructions. We finally compare the effect of parameters controlling mantle viscosity and individual plate speeds to the effect of localized surface processes, such as oceanization and subduction initiation. We infer that studies of Earth's thermal history should focus on surface processes as they appear to be key control parameters.

Effect of Insertion of the Dish on the Behaviour of the Convective Heat Loss

The main contributing factor in analysing the performance of solar parabolic dish system (PDS) is the high amount of heat associated with the higher concentration ratio. To determine the convective heat loss from receiver in real scenario is a challenging task. Installation of these PDS in open environment also causes an escalation in the convection heat loss due to diverse wind circumstances. This work is aimed at providing quantitative insight into examine the heat loss behaviour by the insertion of the dish structure. The study is numerically performed using different wind velocities and attacking angles with constant cavity wall temperature. Free convection study was performed for ranges 0°–90° tilt angle and found s strong dependence of heat loss on the orientation of the dish. While in forced convection cases, different wind incidence angles in addition to tilt angles were examined from 1 to 20 m/s. The detailed convective heat loss patterns provided a clear picture of the effect of the dish. The convective heat loss was drastically changed due to the coupled dish–receiver flow interaction in almost all cases. As a result, the convective heat losses can be described as the function of the orientation of the dish–receiver system. However, the maximum heat loss occurs at zero degree tilt angle during forced convection irrespective of wind incidence angle Also, a critical velocity, depending upon the operating conditions of parabolic dish system, was observed to shift the flow from the mixed convection to forced convection flow.